This study will investigate the independent and interactive effects of soy an probiotic consumption on lipids and estrogen and phytoestrogen metabolism in women who have had breast cancer and controls. A randomized, cross-over human study will be performed, in which 20 post-menopausal breast cancer survivors and 20 post-menopausal controls will consume 4 different combinations of dietary supplements for six weeks each, separated by 2-week washout periods. The supplements will be: 1) soy powder containing 2mg phtoestrogens per kg body weight + placebo capsule; 2) casein powder + probiotic capsule; 3) soy powder containing 2mg phytoestrogen per kg body weight + probiotic capsule; 4) casein powder + placebo capsule. Urine (3, 24 hour samples) and one fasting blood draw will be collected at the beginning of the study and the end of each diet period. Samples will be evaluated for lipoproteins as well as urinary and blood estrogen and phytoestrogen metabolites. To assure that energy and nutrient intakes do not differ between diet periods, food records will be collected once at the beginning of the study and at the end of each diet period. Feces will be collected once before the study begins and once at the end of each diet period, for evaluation of intestional microflora profiles.